Pressure sensitive adhesive compositions are blends of several raw materials including elastomers, resins, plasticizers and other additives such as antioxidants, fillers, pigments, etc. Since these ingredients must be blended in the proper ratio to obtain the adhesive having the desired properties, the raw materials are typically blended with a mechanical mixer under controlled conditions as part of a batch-wise process to obtain a thoroughly mixed product having the appropriate relative amounts of the raw materials.
Planetary roll extruders have been known and have typically been used in processing of thermoplastics such as PVC, for example, where they were used primarily to supply the downstream units such as, for example, calenders or roll mills. Planetary roll extruders have typically been used to process heat-sensitive compounds with a minimum of degradation because thin layers of compound can be exposed to large surface areas thereby resulting in effective heat exchange, mixing and temperature control. Planetary roll extruders are available in various designs and sizes. The diameters of the roll cylinders, depending on the desired throughput, are typically between 70 mm and 500 mm.
Planetary roll extruders generally have a filling section and a compounding section. The filling section typically includes a conveying screw to which certain raw materials are fed continuously. The conveying screw then passes the material to the compounding section. The compounding section includes a driven main spindle and a number of planetary spindles which rotate around the main spindle within a roll cylinder with internal helical gearing. The rotary speed of the main spindle and hence the rotational speed of the planetary spindles can be varied and is one parameter to be controlled during the compounding process. The materials are circulated between the main and planetary spindles, or between the planetary spindles and the helical gearing of the roll section, so that under the materials are dispersed to form a homogeneous composition.
The number of planetary spindles rotating in each roll cylinder can be varied and thus adapted to the requirements of the process. The number of spindles influences the free volume within the planetary roll extruder, the residence time of the material in the process, and also determines the surface area for heat and material exchange. By way of the dispersive energy introduced, the number of planetary spindles has an influence on the result of compounding. Given a constant diameter of roll cylinder, a larger number of spindles permit better homogenization and dispersion or, respectively, a greater product throughput.
The maximum number of planetary spindles installable between the main spindle and the roll cylinder depends on the diameter of the roll cylinder and on the diameter of the planetary spindles used. When using relatively large roll diameters, as required for obtaining production-scale throughputs, and/or relatively small diameters for the planetary spindles, the roll cylinders can be equipped with a relatively large number of planetary spindles. With a roll diameter of D=70 mm, typically up to seven planetary spindles are used, whereas with a roll diameter of D=200 mm ten, for example, and a roll diameter of D=400 mm 24 for example, planetary spindles can be used. However, these examples are in no way limiting to those skilled in the art. For example, if the diameter of the main spindle is smaller relative to a larger main spindle, the number of planetary spindles can be increased.